Electroconductive composition

Abstract

This electroconductive composition is characterized by comprising an epoxy resin, an imidazole-based curing agent containing no triazine ring, a benzoxazine resin, and electroconductive particles, wherein the epoxy resin contains an alicyclic epoxy resin.

Description

conductive composition CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2023-186219, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an electrically conductive composition.

[0003] Conventionally, printed wiring boards have been produced by etching copper-clad laminates, which are made by laminating copper foil on an electrically insulating substrate, and then soldering electronic elements such as LSIs and capacitors to the printed wiring board to produce printed circuit boards. Known printed wiring boards used in this type of printed circuit board include rigid boards, which have a substrate made of glass cloth impregnated with epoxy resin, as well as flexible boards and film boards, which use polyimide film, polyethylene terephthalate resin film, or the like as substrates. Known types of printed wiring boards include single-sided boards, in which wiring is provided on only one side of the substrate; double-sided boards, in which wiring is provided on both sides of the substrate; and multilayer boards, in which multiple substrates are alternately laminated with wiring. Among these, double-sided boards and multilayer boards often have through-holes that penetrate the substrate in the thickness direction, allowing electrical connections between layers to be made through the through-holes.

[0004] Recently, there has been an increase in the use of printing methods that use conductive compositions instead of copper foil to form wiring on substrates, and in the use of conductive compositions instead of soldering to electrically connect electronic elements to wiring. Known conductive compositions of this type include those containing conductive particles, such as silver particles, and a curable resin. When used as a wiring agent, such conductive compositions do not require complex processes such as etching copper foil, and when used as a conductive adhesive, they do not require high-temperature processes such as soldering, making them highly convenient.

[0005] Meanwhile, heat dissipation measures have become an issue due to the miniaturization of electronic devices and packages resulting from high-density mounting. The conventional approach to heat dissipation is to plate the walls of through holes that penetrate the substrate in the thickness direction, but even this approach has proven difficult to ensure sufficient heat dissipation. Therefore, there has been a demand for methods such as using highly thermally conductive materials to further improve heat dissipation while still maintaining good electrical conductivity.

[0006] Patent Document 1 discloses an invention of a conductive paste containing copper powder as conductive powder and a compound having a benzoxazine ring, and it is said that the invention of Patent Document 1 can obtain good durability and conductivity.

[0007] Japanese Patent Application Publication No. 2017-4712

[0008] In the invention of Patent Document 1, good electrical conductivity can be obtained, but sufficient consideration has not been given to the evaluation of heat dissipation properties.

[0009] Therefore, an object of the present invention is to provide a conductive composition that has both excellent electrical conductivity and thermal conductivity.

[0010] The conductive composition according to the present invention comprises an epoxy resin, an imidazole-based curing agent containing no triazine ring, a benzoxazine resin, and conductive particles, wherein the epoxy resin contains an alicyclic epoxy resin.

[0011] 1a shows a side view of two tough-pitch copper plates overlapping each other in an adhesion evaluation test for a conductive composition, and FIG. 1b shows a front view of two tough-pitch copper plates overlapping each other in an adhesion evaluation test for a conductive composition.

[0012] Hereinafter, a conductive composition according to one embodiment of the present invention will be described.

[0013] The conductive composition of the present embodiment includes a curable resin composition and conductive particles.

[0014] The curable resin composition has reaction curing properties. In the conductive composition according to this embodiment, the curable resin composition has thermosetting properties. The conductive composition according to this embodiment is liquid when the curable resin composition is in an uncured state. In this specification, the term "liquid" does not only mean a low-viscosity composition that exhibits fluidity under the action of gravity at room temperature (25°C), but also includes a semi-solid state such as a paste state.

[0015] In the conductive composition according to this embodiment, the curable resin composition is applied to an adherend in an uncured state and then cured to form a cured product with excellent electrical and thermal conductivity. The curable resin composition can be applied to the adherend by printing, transfer, spraying, or other methods, or spot-applied using a dispenser. The curable resin composition can be used to form the wiring of an electrical or electronic circuit. In this case, examples of the adherend to which the curable resin composition is applied include metal materials such as copper foil; and insulating materials (electrical insulating sheets) such as epoxy resin-impregnated glass sheets, polyimide resin sheets, polyethylene terephthalate resin sheets, and ceramic sheets. When used as a constituent material for a circuit board, the curable resin composition according to this embodiment can be used as a wiring material, a bonding material for electrically connecting wiring and electronic elements instead of soldering, a filler for filling through holes, and the like.

[0016] In the conductive composition according to this embodiment, the curable resin composition can be cured at a temperature lower than the melting point of the solder (for example, 180°C or lower). The curable resin composition according to this embodiment can be particularly useful in situations where the adherend is a polyethylene terephthalate resin sheet, which has a lower softening temperature than a polyimide resin sheet or the like. Polyethylene terephthalate resin has a high affinity with epoxy resins and exhibits good wettability with the curable resin composition. Therefore, the adherend to which the curable resin composition according to this embodiment is attached may have at least the adherend surface to which the curable resin composition is attached composed of a resin composition containing polyethylene terephthalate resin.

[0017] The surface of the adherend may be subjected to a surface treatment such as a mechanical surface treatment to enhance the anchoring effect, such as hairline finishing or matte finishing, an electrical surface treatment to increase functional groups such as hydroxyl groups on the surface, such as plasma treatment or corona treatment, or a coating with a primer, a coupling agent, or the like.

[0018] In the conductive composition according to this embodiment, the curable resin composition can also be used as a conductive adhesive for purposes other than circuit formation, and can also be used as a thermally conductive adhesive primarily intended for heat dissipation purposes.

[0019] In the conductive composition according to the present embodiment, the curable resin composition includes an epoxy resin and a curing agent. The curable resin composition may optionally include a solvent, an additive, and the like.

[0020] From the viewpoint of work efficiency in the coating process, the curable resin composition preferably has a low viscosity. One method for lowering the viscosity of the curable resin composition is to use an optional solvent. However, volatile substances such as solvents not only deteriorate the work environment, but also may cause molding defects in the cured product of the curable resin composition due to the evaporation of the solvent. To prevent such problems, the curable resin composition is preferably composed of a solvent-free conductive composition.

[0021] The epoxy resin includes an alicyclic epoxy resin. The epoxy resin may further include at least one of an aromatic epoxy resin and an aliphatic epoxy resin. The alicyclic epoxy resin has an alicyclic skeleton and an epoxy group. The alicyclic skeleton includes a cycloalkane such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, or cyclodecane. The alicyclic skeleton also includes a polycyclic skeleton such as decalin, norbornane, or dicyclopentadiene. The alicyclic epoxy resin preferably has a dicyclopentadiene skeleton as the alicyclic skeleton.

[0022] The epoxy resin contains the alicyclic epoxy resin, which allows for a variety of orientations of the epoxy groups in the epoxy resin. That is, the epoxy groups can be oriented in the axial (vertical) or equatorial (horizontal) direction relative to the alicyclic skeleton. This allows the resin derived from the alicyclic epoxy resin to form three-dimensional steric crosslinks when the conductive paste hardens. Because cure shrinkage occurs based on the steric crosslinks, the conductive composition can achieve good conductivity.

[0023] The alicyclic epoxy resin preferably has two or more epoxy groups. The alicyclic epoxy resin may have three or more epoxy groups. The upper limit of the number of epoxy groups contained in the alicyclic epoxy resin is not particularly limited, but is usually six or less.

[0024] Since the alicyclic epoxy resin has two or more epoxy groups, when the resin derived from the alicyclic epoxy resin forms three-dimensional crosslinks by curing, the distance between adjacent crosslinks in the cured epoxy resin becomes short. This allows the cured epoxy resin to have a highly three-dimensional crosslinked structure. Therefore, the conductive composition can obtain excellent electrical and thermal conductivity.

[0025] The alicyclic epoxy resin may have a glycidyl group as the epoxy group. The free rotation derived from the methylene bond contained in the glycidyl group gives flexibility to the configuration of the epoxy moiety in the glycidyl group, allowing the epoxy moiety to react efficiently during curing. Therefore, it is preferable that the alicyclic epoxy resin has a glycidyl group.

[0026] When the content of the epoxy resin in the curable resin composition is taken as 100.0 parts by mass, the content of the alicyclic epoxy resin is preferably 10.0 parts by mass or more, more preferably 30.0 parts by mass or more, even more preferably 50.0 parts by mass or more, and particularly preferably 70.0 parts by mass or more. There is no particular upper limit for the content of the alicyclic epoxy resin in the epoxy resin, and the epoxy resin may be composed solely of the alicyclic epoxy resin.

[0027] The epoxy resin may include an aromatic epoxy resin. The aromatic epoxy resin has an aromatic backbone and an epoxy group. Examples of the epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, tetrabromobisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol S-type epoxy resin; glycidyl ether-type epoxy resins such as tris(glycidyloxyphenyl)methane and tetrakis(glycidyloxyphenyl)ethane; glycidylamine-type epoxy resins such as N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis(N,N-diglycidylaniline); and novolac-type epoxy resins such as cresol novolac-type epoxy resin, phenol novolac-type epoxy resin, α-naphthol novolac-type epoxy resin, and brominated phenol novolac-type epoxy resin. By including the aromatic epoxy resin in the epoxy resin, the conductive composition can achieve excellent durability and heat resistance.

[0028] The aromatic epoxy resin preferably has two or more epoxy groups. The aromatic epoxy resin may have three or more epoxy groups. The upper limit of the number of epoxy groups in the aromatic epoxy resin is not particularly limited, but is usually six or less. The aromatic epoxy resin may be liquid or solid at room temperature (25°C). The aromatic epoxy resin being liquid at room temperature (25°C) is advantageous in terms of providing the curable resin composition with good printability and through-hole filling properties.

[0029] The aromatic epoxy resin may contain, as the epoxy group, a glycidyl group or a diglycidylamino group in addition to the epoxy group. The aromatic epoxy resin preferably contains a diglycidylamino group. The diglycidylamino group can increase the number of epoxy groups contained in one molecule, and the bond angle derived from the nitrogen atom in the amino group can three-dimensionally orient the glycidyl groups. Therefore, when the aromatic epoxy resin contains a diglycidylamino group, the resin derived from the aromatic epoxy resin can form three-dimensional steric crosslinks when the conductive paste is cured. The cure shrinkage due to the steric crosslinks allows the conductive composition to achieve good conductivity.

[0030] When the content of the epoxy resin in the curable resin composition is taken as 100.0 parts by mass, the content of the aromatic epoxy resin is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less. There is no particular limitation on the lower limit of the content of the aromatic epoxy resin in the epoxy resin, but the aromatic epoxy resin may be contained in a proportion of, for example, 10.0 parts by mass or more, or 20.0 parts by mass or more.

[0031] The epoxy resin may contain an aliphatic epoxy resin as a reactive diluent. The aliphatic epoxy resin has an aliphatic portion and an epoxy group. The aliphatic portion may have a linear or branched structure. The aliphatic portion may be composed of saturated or unsaturated bonds. The aliphatic portion may have from 1 to 10 carbon atoms. The reactive diluent is preferably one in which the aliphatic portion has a linear structure and has 5 or 6 carbon atoms. Examples of the reactive diluent include those that are liquid at room temperature (25°C), such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and 1,6-hexanediol diglycidyl ether.

[0032] When the content of the epoxy resin in the curable resin composition is taken as 100.0 parts by mass, the content of the aliphatic epoxy resin is preferably 30.0 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10.0 parts by mass or less. There is no particular limitation on the lower limit of the content of the aliphatic epoxy resin in the epoxy resin, and the aliphatic epoxy resin may be contained in a proportion of, for example, 1.0 part by mass or more, or 5.0 parts by mass or more.

[0033] The epoxy equivalent of the epoxy resin is preferably 20 g / eq or more, more preferably 80 g / eq or more, and even more preferably 95 g / eq or more. The epoxy equivalent of the epoxy resin is preferably 1300 g / eq or less, more preferably 800 g / eq or less, and even more preferably 300 g / eq or less. Specifically, the epoxy equivalent can be determined by the method described in JIS K 7236:2001 "Determination of epoxy equivalent of epoxy resin."

[0034] In the conductive composition according to this embodiment, the curing agent contains an imidazole-based curing agent that does not contain a triazine ring and a benzoxazine resin.

[0035] The imidazole curing agent forms a tertiary amine by reacting the nitrogen atom on the imidazole ring with the epoxy group. The tertiary amine acts as a catalyst to accelerate the curing of the epoxy resin. This catalytic action increases the curing rate and suppresses the generation of unreacted residual epoxy resin and gelation.

[0036] The number of carbon atoms in the alkyl group is preferably 1 or more, more preferably 5 or more, and even more preferably 10 or more. The number of carbon atoms in the alkyl group is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less.

[0037] The alkyl group may be substituted on the imidazole ring at position 2, 4, or 5. One imidazole ring may be substituted with multiple alkyl groups.

[0038] The imidazole curing agent is preferably composed of one or more compounds selected from the group consisting of 2-n-heptadecylimidazole, 2-n-undecylimidazole, 1-(2-cyanoethyl)-2-n-undecylimidazole, 4-methyl-2-phenylimidazole, 5-(hydroxymethyl)-4-methyl-2-phenylimidazole, and 4,5-bis(hydroxymethyl)-2-phenylimidazole.The imidazole curing agent is more preferably composed of one or more compounds selected from the group consisting of 2-n-heptadecylimidazole, 2-n-undecylimidazole, and 1-(2-cyanoethyl)-2-n-undecylimidazole.

[0039] The content of the imidazole curing agent relative to 100.0 parts by mass of the epoxy resin is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and preferably 20.0 parts by mass or less, more preferably 16.0 parts by mass or less, and even more preferably 12.0 parts by mass or less, relative to 100.0 parts by mass of the epoxy resin.

[0040] When the benzoxazine resin is heated, the benzoxazine ring opens and undergoes a polymerization reaction (hereinafter referred to as "ring-opening polymerization"). The ring-opening polymerization of the benzoxazine resin produces a novolac phenolic resin having a phenolic hydroxyl group and a tertiary amine. The novolac phenolic resin acts as a curing accelerator for the epoxy resin. More specifically, the phenolic hydroxyl group or tertiary amine of the novolac phenolic resin reacts with the epoxy resin, and the tertiary amine then acts as a catalyst to accelerate the curing of the epoxy resin.

[0041] Examples of the benzoxazine resin include P-d type benzoxazine, Fa type benzoxazine, and ALPd type benzoxazine. Resins having a benzoxazine structure are not particularly limited, and examples include a reaction product of bisphenol F, formalin, and aniline (Fa type benzoxazine resin), a reaction product of diaminodiphenylmethane, formalin, and phenol (P-d type benzoxazine resin), a reaction product of bisphenol A, formalin, and aniline, a reaction product of dihydroxydiphenyl ether, formalin, and aniline, a reaction product of diaminodiphenyl ether, formalin, and phenol, a reaction product of dicyclopentadiene-phenol addition resin, formalin, and aniline, a reaction product of phenolphthalein, formalin, and aniline, a reaction product of diphenyl sulfide, formalin, and aniline, and a reaction product of diaminodiphenylmethane, formalin, and a phenol having an allyl group (ALPd type benzoxazine resin). These may be used alone, or two or more types may be used in combination. Among these, the benzoxazine resin is particularly preferably a Pd type benzoxazine resin, an Fa type benzoxazine resin, or an ALPd type benzoxazine resin.

[0042] The content of the benzoxazine resin is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, relative to 100.0 parts by mass of the epoxy resin, and is preferably 29.0 parts by mass or less, more preferably 27.0 parts by mass or less, and even more preferably 25.0 parts by mass or less, relative to 100.0 parts by mass of the epoxy resin.

[0043] Examples of the conductive particles include copper particles, silver particles, nickel particles, silver-coated copper particles, nickel-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, and solder particles (including not only those made of an alloy primarily composed of lead and tin, but also so-called lead-free solder). Two or more different particles may be used simultaneously as the conductive particles. The conductive particles are preferably either silver-coated copper particles or silver particles.

[0044] The shape of the conductive particles is not particularly limited, but examples thereof include spherical, flake, spike, polyhedral, and dendritic shapes. The average particle size of the conductive particles is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. The average particle size of the conductive particles is preferably 15.0 μm or less, more preferably 6.0 μm or less, and even more preferably 4.0 μm or less.

[0045] When the average particle size of the conductive particles is less than 0.5 μm, the specific surface area of ​​the conductive particles increases, and many of the monomers, such as epoxy resins, contained in the conductive composition interact with the conductive particles, reducing the amount of freely movable monomers. This results in a problem of reduced fluidity of the conductive paste composed of the conductive composition. On the other hand, when the average particle size of the conductive particles exceeds 15.0 μm, the contact area between the conductive particles decreases, resulting in reduced electrical conductivity and thermal conductivity. Therefore, by having the average particle size of the conductive particles be 0.5 μm or more and 15.0 μm or less, the conductive paste can be ensured to have good fluidity and exhibit good electrical conductivity and thermal conductivity. The average particle size of the conductive particles can be determined, for example, as the median diameter (D50) in a cumulative particle size distribution curve on a volume basis measured by laser diffraction scattering.

[0046] The content of the conductive particles in the conductive composition (hereinafter referred to as "conductive particle loading") is 77% by mass or more, more preferably 80% by mass or more, and even more preferably 83% by mass. The conductive particle loading is 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less.

[0047] The conductive composition may further include a third curing agent other than the first curing agent consisting of one or more imidazole-based curing agents and the second curing agent consisting of one or more benzoxazine resins. Examples of the third curing agent include amine-based curing agents, acid anhydride-based curing agents, thiol-based curing agents, and phenol-based curing agents. The third curing agent is preferably one or more phenol-based curing agents.

[0048] The content of the third curing agent is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, relative to 100.0 parts by mass of the epoxy resin. The content of the third curing agent is preferably 24.0 parts by mass or less, more preferably 22.0 parts by mass or less, and even more preferably 20.0 parts by mass or less, relative to 100.0 parts by mass of the epoxy resin.

[0049] The total amount of the first curing agent (the imidazole curing agent), the second curing agent (the benzoxazine resin), and the third curing agent (hereinafter referred to as the "curing agent amount") relative to 100 parts by mass of the epoxy resin is preferably 5 parts by mass or more, more preferably 10 parts by mass or more. The curing agent amount relative to 100 parts by mass of the epoxy resin is preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

[0050] The solvent preferably has a boiling point of about 150 to 250° C., and examples thereof include esters such as γ-butyrolactone and propylene carbonate, and ethers such as butyl carbitol. The curable resin composition may contain only one type of solvent, or may contain multiple types of solvents.

[0051] The content of the solvent is preferably 1.0 part by mass or more and 10.0 parts by mass or less with respect to 100.0 parts by mass of the epoxy resin contained in the curable resin composition.

[0052] Examples of the additives include colorants such as pigments, plasticizers, flame retardants, antioxidants, antifoaming agents, adhesion promoters, leveling agents, rheology control agents, inorganic fillers which are inorganic particles other than the conductive particles, etc. The content of the additives is, for example, 0.5 parts by mass or more and 20.0 parts by mass or less relative to 100.0 parts by mass of the epoxy resin contained in the curable resin composition.

[0053] The conductive composition can be applied to a substrate and then subjected to a heating step to form a cured product. The resistivity value of the cured product is preferably 5E-04 Ω cm or less, more preferably 1E-04 Ω cm or less, and even more preferably 0.8E-04 Ω cm or less. The lower the resistivity value of the cured product, the better the conductivity, so there is no particular limit on the lower limit of the resistivity value of the cured product. The resistivity value of the cured product can be measured by the following method.

[0054] <Method of measuring specific resistance> The conductive composition of each example was printed in lines (length 60 mm, width 1 mm, thickness approximately 100 μm) on a glass epoxy substrate (glass sheet impregnated with epoxy resin) using a metal plate, and then heated at 80°C for 30 minutes for temporary curing, and then heated at 160°C for 60 minutes for full curing to prepare an evaluation substrate on which a conductive pattern was formed. Next, the resistance value R (Ω) between both ends of the conductive pattern was measured using a tester. The cross-sectional area S (cm ２ ) and length L (cm) are used to calculate the resistivity using the following formula (1). Five lines are printed on each of three glass epoxy boards to form a total of 15 conductive patterns, and the average value of the resistivity is calculated. Resistivity (Ω cm) = Cross-sectional area S (cm ２ ) / length L (cm) × resistance value R (Ω) ... (1)

[0055] The thermal conductivity of the cured product is preferably 10 W / m K or more, more preferably 15 W / m K or more, and even more preferably 20 W / m K or more. The higher the thermal conductivity of the cured product, the better the heat dissipation performance, so the upper limit is not particularly limited. The thermal conductivity of the cured product can be measured by the following method.

[0056] <Method for measuring thermal conductivity> The conductive composition is heated at 80°C for 30 minutes for provisional curing, and then heated at 160°C for 60 minutes for full curing to produce a cured product having a length of 25 mm, a width of 25 mm, and a thickness of 250 μm. ２ The density ρ (g / cm ３ ) is measured using an electronic balance by the immersion method based on Archimedes' principle. The specific heat capacity Cp (J / g·K) is measured using a Perkin Elmer differential scanning calorimeter "DSC8500". The thermal conductivity λ (W / m·K) is calculated using the following formula (2): Thermal conductivity λ (W / m·K) = Thermal diffusivity α (mm ２ / s)×density ρ(g / cm ３ ) × specific heat capacity Cp (J / g K) ... (2)

[0057] The conductive resin composition shrinks during curing, improving the durability of the cured product and promoting contact between the conductive particles, thereby ensuring good conductivity.

[0058] The above examples of the conductive composition of this embodiment are merely restrictive examples, and the present invention is not limited to the above examples in any way, and can be carried out by making appropriate modifications to the above examples. As described above, this embodiment includes the following disclosures.

[0059] [1] A conductive composition comprising an epoxy resin, an imidazole-based curing agent not containing a triazine ring, a benzoxazine resin, and conductive particles, wherein the epoxy resin contains an alicyclic epoxy resin.

[0060] According to this configuration, the conductive composition can have excellent electrical conductivity and excellent thermal conductivity.

[0061] [2] The conductive composition according to [1], wherein the imidazole-based curing agent has an alkyl group.

[0062] According to this configuration, the conductive composition can have better electrical conductivity and better thermal conductivity.

[0063] [3] The conductive composition according to [1] or [2], wherein the alicyclic epoxy resin has two or more epoxy groups.

[0064] According to this configuration, the conductive composition can have better electrical conductivity and better thermal conductivity.

[0065] [4] The conductive composition according to [3], wherein the epoxy group is a glycidyl group.

[0066] According to this configuration, the conductive composition can have better electrical conductivity and better thermal conductivity.

[0067] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0068] Example 1 Preparation of Conductive Composition 60.0 parts by mass of aromatic epoxy resin A1a, 30.0 parts by mass of alicyclic epoxy resin A2a, 10.0 parts by mass of aliphatic epoxy resin A3 as a reactive diluent, 1.5 parts by mass of imidazole-based curing agent B1, 5.0 parts by mass of a phenol-based curing agent, 10.0 parts by mass of benzoxazine resin D1, and 779.7 parts by mass of conductive particles E1 were blended and mixed to prepare a conductive composition.

[0069] (Examples 2 to 27, Comparative Examples 1 to 6, Reference Examples 1 to 3) In Examples 2 to 27, Comparative Examples 1 to 6, and Reference Examples 1 to 3, conductive compositions were prepared in the same manner as in Example 1, except that the types and amounts of the aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, imidazole-based curing agent, phenol-based curing agent, benzoxazine resin, and conductive particles were changed to those shown in Tables 1 to 5, respectively.

[0070] Details of the components used in each example are as follows: Aromatic Epoxy Resins (A1a): Glycidylamine-type epoxy resin (epoxy equivalent: 100 g / eq, liquid) (A1b): Bisphenol A-type epoxy resin (epoxy equivalent: 190 g / eq, liquid) (A1c): Bisphenol F-type epoxy resin (epoxy equivalent: 170 g / eq, liquid) Alicyclic Epoxy Resins (A2a): Dicyclopentadiene-type epoxy resin (epoxy equivalent: 180 g / eq, liquid) (A2b): Dicyclopentadiene-type epoxy resin (epoxy equivalent: 290 g / eq, solid) Aliphatic Epoxy Resins (A3): Reactive Diluent (135 g / eq, liquid) Imidazole-Based Curing Agents (B1): 2-n-Heptadecylimidazole (Curezol (registered trademark) C17Z, manufactured by Shikoku Chemicals Corporation) (B2): 2-n-undecylimidazole (manufactured by Shikoku Chemical Industry Corporation: Curazol (registered trademark) C11) (B3): 1-(2-cyanoethyl)-2-n-undecylimidazole (manufactured by Shikoku Chemical Industry Corporation: Curazol (registered trademark) C11Z-CN) (B4): 4-methyl-2-phenylimidazole (manufactured by Shikoku Chemical Industry Corporation: Curazol (registered trademark) 2P4MZ) (B5): 5-(hydroxymethyl)-4-methyl-2-phenylimidazole (manufactured by Shikoku Chemical Industry Corporation: Curazol (registered trademark) 2P4MHZ) (B6): 4,5-bis(hydroxymethyl)-2-phenylimidazole (manufactured by Shikoku Chemical Industry Corporation: Curazol (registered trademark) 2PHZ) (B7): 2-methyl-1-(2-(4,6-diamino-1,3,5-triazin-2-yl)ethyl)imidazole (manufactured by Shikoku Chemical Industry Co., Ltd.: Curesol (registered trademark) 2MZ-A) {Curing agent} (C): Phenol-based curing agent (manufactured by Arakawa Chemical Industries, Ltd.: "Tamanol 759") {Benzoxazine resin} (D1): P-d-type benzoxazine (D2): Fa-a-type benzoxazine (D3): ALPd-type benzoxazine Conductive particles (E) (E1): Silver-coated copper particles, spherical, average particle size: 4 to 6 μm (E2): Silver-coated copper particles, spherical, average particle size: 2 to 3 μm (E3): Silver powder, spherical, average particle size: 4 to 6 μm (E4): Silver powder, spherical, average particle size: 2 to 3 μm

[0071] <Evaluation of resistivity> The resistivity (Ω·cm) of each example was measured by the method described above. <Evaluation criteria> Excellent: Resistivity is 0.8E-04 Ω·cm or less. Good: Resistivity is greater than 0.8E-04 Ω·cm and less than 1E-04 Ω·cm. Passable: Resistivity is greater than 1E-04 Ω·cm and less than 5E-04 Ω·cm. Poor: Resistivity exceeds 5E-04 Ω·cm.

[0072] <Evaluation of thermal conductivity> The thermal conductivity λ (W / m·K) of each example was measured using the method described above. <Evaluation criteria> Excellent: Thermal conductivity is 20 W / m·K or more. Good: Thermal conductivity is 15 W / m·K or more and less than 20 W / m·K. Fair: Thermal conductivity is 10 W / m·K or more and less than 15 W / m·K. Unacceptable: Thermal conductivity is less than 10 W / m·K.

[0073] The type and content of the imidazole-based curing agent, which is a component of the conductive composition, were investigated and evaluated, and the results are shown in Table 1 below.

[0074]

[0075] The results in Table 1 show that when the imidazole curing agent (B7) having a triazine ring was used, the cured product of the conductive composition exhibited insulating properties. On the other hand, when the imidazole curing agents (B1) to (B6) were used, good results were obtained in the evaluation of resistivity and thermal conductivity.

[0076] The type and content of the benzoxazine resin, which is a component of the conductive composition, and the content of the curing agent were investigated and evaluated, and the results are shown in Table 2 below.

[0077]

[0078] The results in Table 2 show that good thermal conductivity cannot be achieved without the benzoxazine resin. When the benzoxazine resins (D1) to (D3) were used, good results were obtained in the evaluation of resistivity and thermal conductivity.

[0079] The type and content of the epoxy resin, which is a component of the conductive composition, were investigated and evaluated, and the results are shown in Table 3 below.

[0080]

[0081] The results in Table 3 show that good thermal conductivity cannot be achieved when the alicyclic epoxy resin is not included. In addition, the higher the content of the alicyclic epoxy resin, the better the results obtained in the evaluation of resistivity and thermal conductivity.

[0082] The type, particle size, and content of the conductive particles, which are components of the conductive composition, were investigated and evaluated, and the results are shown in Table 4 below.

[0083]

[0084] According to the results in Table 4, the smaller the particle size of the conductive particles and the greater the content of the conductive particles, the better the results obtained in the evaluation of resistivity and thermal conductivity.

[0085] The results of examining and evaluating the curing agent, which is a component of the conductive composition, are shown in Table 5 below as reference examples. In the reference examples in Table 5, thermal conductivity and adhesion were evaluated. The adhesion test method is as follows.

[0086] <Evaluation of Conductive Composition: Adhesion> A tough-pitch copper plate 1 (length 100 mm, width 25 mm, thickness 1.6 mm) specified in JIS H 3100 was used. As shown in Figures 1a and 1b, the conductive composition was applied to an area (adhesion area 2) 12.5 mm ± 0.5 mm from the end of tough-pitch copper plate 1, and two tough-pitch copper plates were bonded together. The composition was pre-cured by heating at 80°C for 30 minutes, and then fully cured by heating at 180°C for 60 minutes to prepare a test specimen. A tensile test was performed using a tensile tester, with the test specimen gripped in areas 38.0 mm ± 1.0 mm from both ends (gripping area 3) as shown in Figure 1b. The maximum load until the test specimen broke was measured, and the shear adhesive strength was calculated using the following formula (3): shear adhesive strength (MPa) = maximum load (N) / shear area of ​​test specimen (mm ２ ) (3) <Evaluation Criteria> Good: The shear adhesive strength is 5 MPa or more. Fair: The shear adhesive strength is 3 MPa or more and less than 5 MPa. Poor: The shear adhesive strength is less than 3 MPa.

[0087]

[0088] According to the results in Table 5, good thermal conductivity and adhesion were obtained in each of the reference examples.

[0089] From the above, it can be seen that the present invention can provide a conductive composition that has both excellent electrical conductivity and thermal conductivity.

[0090] 1: Tough pitch copper plate, 2: Adhesive area, 3: Gripping area

Claims

1. A conductive composition comprising an epoxy resin, an imidazole-based curing agent not containing a triazine ring, a benzoxazine resin, and conductive particles, wherein the epoxy resin contains an alicyclic epoxy resin.

2. The conductive composition according to claim 1, wherein the imidazole-based curing agent has an alkyl group.

3. The conductive composition according to claim 1, wherein the alicyclic epoxy resin has two or more epoxy groups.

4. The conductive composition according to claim 3, wherein said epoxy group is a glycidyl group.

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